1. Technical Field
The present invention relates to a lead-free plain bearing material having a matrix on the basis of CuFe2P. The invention further relates to a plain bearing composite material comprising a steel support layer and a bearing layer made of such a CuFe2P plain bearing material and a sliding member on the basis of CuFe2P.
2. Related Art
Lead-free sintered plain bearing materials on the basis of copper, especially on the basis of a bronze matrix, are well known for favourable heat conductivity and high wear and corrosion resistance when compared to similar materials containing lead. The development of such materials resulted from the desire to replace plain bearing materials containing lead as lead has been classified as a contaminant harmful to the environment. Lead in a plain bearing material has the function of a solid lubricant. Hence a replacement is needed for said solid lubrication. Otherwise, a one-phase bronze material may have increased susceptibility to seizing under mixing friction conditions. Under this aspect, a number of different compositions have been examined both in literature and practical applications and put to use.
For example, EP 0 962 541 A1 describes a copper-based sliding material wherein particles of AlN, Al2O3, NiB, Fe2B, SiC, TiC, WC, Si3N4, Fe3P, Fe2P and/or Fe3B are dispersed in a matrix of sintered copper or a sintered copper alloy. In order to prepare the sliding material, a copper or copper alloy powder is mixed with, for example, AlN (Hv: 1,300, particle diameter e.g. 0.5 μm) and Fe3P particles (Hv: 800; particle diameter e.g. 5 μm) and the mixture subjected to sintering. The weight ratio and the average particle diameter of the particles having a mean hardness (Hv) of 500 to 1,000 (i.e. Fe3P, Fe2P and/or Fe3B) in the mixture and in the sliding material are selected in such a manner that they are larger than the weight ratio and the average particle diameter of the high-hardness (Hv) particles of 1,100 or more (i.e. AlN, Al2O3, NiB, Fe2B, SiC, TiC, WC and/or Si3N4).
Another copper-based sliding material is described in WO 2008/140100. It contains 1.0 to 15 wt.-% of Sn, 0.5 to 15 wt.-% of Bi and 0.05 to 5 wt.-% of Ag, Ag and Bi being present in a eutectic state. If necessary, the sliding material may contain 1 to 10 wt.-% of Fe3P, Fe2P, FeB, NiB and/or AlN particles having an average grain diameter of 1.5 to 70 μm.
In contrast to the above, CuFe2P has primarily been used in the electronics industry (e.g. as a contact material) and as a heat exchanger material. US 2009/0010797, for example, describes a plate for electronic components made of a Cu—Fe—P alloy containing 0.01 to 3 wt.-% of Fe and 0.01 to 0.3 wt.-% of P and having a special orientation. CuFe2P is mentioned as a suitable copper alloy. US 2006/0091792 describes sputter targets for flat-screens made of special Cu—Fe—P alloys.